The Screaming Man is a biological humanoid that, whenever it attempts to open its mouth, instead of its normal voice being heard, several different voices are heard, all of which are usually in either distress or begging for forgiveness in some form or another. These voices are only heard when the subject opens its mouth.
The man was found in prison, after he had murdered his entire family. The voices are that of his family. He is forced to hear their screams and begs of forgiveness as crime for his punishment.